The MCZ (magnetic field applied Czochralski) method and the FZ (floating zone) method have been widely used to produce silicon wafers. These silicon wafers are used to manufacture various semiconductor devices.
When such a silicon wafer is produced and used to manufacture a semiconductor device, the wafer is subjected to an oxidation diffusion process at an elevated temperature, which causes oxygen to enter into and remain in the wafer as dissolved oxygen.
When the silicon substrate (or wafer) is heat treated at a low temperature during the semiconductor device manufacturing process, the dissolved oxygen forms thermal donors, thereby changing the resistivity of the silicon substrate. Therefore, it is desirable to reduce the amount of oxygen dissolved into the silicon substrate as much as possible during the wafer production process and the semiconductor device manufacturing process (see, e.g., Patent Document 1 below).    Patent Document 1: JP-A-2005-145744